Clean air cutting

Major advances in CO2 laser cutting are getting fewer and further apart. High-power lasers are available to cut thicker materials or thinner materials faster, but there is still a need to cut faster, cheaper or better using existing power level lasers. Here we describe a method for producing high-quality edges that often eliminates additional finishing operations prior to painting or welding while costing only one-third as much as nitrogen.


These parts are representative of accomplishments using EZ Cut.
Click here to enlarge image

Services to machine tools have long been a source of concern for plant managers and industrial engineers. Most machine tools require three-phase electricity that is relatively clean, that is no more than plus or minus 10 percent variation from the nominal incoming voltage. Variations in the incoming voltage service to the laser can cause the machine to perform poorly and result in excessive down time, lost production and reduced profitability.

The same is true for the incoming air and assist gas supply. Generally compressed air is a vital component to the operation of a CO2 laser machine tool. Low- to medium-pressure air is used as a beam purge in the beam delivery system to prevent external contaminants from entering the enclosed beam path causing changes to the shape, size and propagation characteristics of the laser beam itself. An additional benefit of the beam purge air is to keep the beam delivery optics cleaner, extending the life of the optics.

Medium- to high-pressure air is connected to valves, cylinders and actuators to open and close doors, beam attenuators and clamps. Fixtures and gauge blocks to move or register the material to be processed are actuated using medium- to high-pressure air regulated to the desired pressure. Certain grades of aluminum cut faster with a better edge finish using air as the assist gas than using more expensive high-pressure nitrogen.

In all instances the air supply must be clean, dry and filtered to the laser machine tool manufacturer's recommendations. This is usually clearly spelled out in the pre-installation manual available from the machine tool manufacturer. Too often, users do not verify that their air supply (compressor, filter, regulators and delivery system) meets the requirements of the laser machine tool. An inadequate air supply (just like an inadequate electrical service,) can produce problems that will cause poor machine performance, excessive down time and lost production and profitability.

One solution to this problem is EZ Cut developed by Amada America Inc. (Buena Park, CA), a self-contained unit, which includes a dedicated compressor, refrigerated dryer, liquid and particle filters and reservoir tank to supply all of the clean dry filtered air requirements of a laser up to 4 kW rated output. The air supply meets the entire laser manufacturer's air supply requirements for the beam purge, air assist gas and machine operation. Most dust collectors used with laser cutting machine tools require compressed air to purge the filters. This automatic filter purge sequence enables the dust collector to operate for longer intervals before manual cleaning and or replacement of the filters. The compressed air from EZ Cut accommodates the air supply requirements of the dust collector as well.

The EZ Cut unit can be placed in close proximity to the laser machine tool thereby eliminating the possibility of moisture, particles or rust contaminating the laser from existing steel, galvanized (or worse yet black iron piping) air lines from an existing compressor. Automatic drains are incorporated to provide an egress of moisture from the system and to minimize the number of routine maintenance shut downs.

Any industrious engineer can purchase a compressor to provide the clean dry filtered air requirements for a laser machine tool. It could be assembled for about the same price as purchasing a commercially available unit from a compressor manufacturer. However, another key feature of the EZ Cut system is the ability to provide 95 percent pure nitrogen for most of the demanding assist gas applications of laser cutting steel and stainless steel.

The main element producing the 95 percent pure nitrogen is a membrane module where the compressed air is separated. As air is passed over the bundled hollow fibers within the membrane, nitrogen molecules separate from the oxygen and water molecules resulting in dry nitrogen gas exiting the membrane. A reservoir tank collects the nitrogen storing it ready for use as an assist gas.

Not every application can benefit from using 95 percent pure nitrogen. There are still situations where the metallurgy of the material, the next process of the part or where the part is to be used requires 99.999 percent pure nitrogen as the assist gas. This is the very familiar process called "clean cutting." Clean cutting produces an oxide-free surface on the laser-cut edge of the stainless steel, which is suitable for the most demanding welding applications. The large presence of oxide in the weld zone can produce a brittle weld, porosity or a poor weld cosmetically that will require excessive grinding and polishing. The same is true if the part is to be used in certain medical or sanitary situations where rust or an oxide on the edge of stainless steel is considered a contaminant.

But where a reduced oxide edge in mild steel is required for improved paint adhesion or a gold-colored tint on the edge of stainless steel is acceptable, the 95 percent pure nitrogen output from EZ Cut is an ideal application. Not only will it provide a significantly reduced oxide edge, but it also eliminates subsequent operations prior to painting.

For the precision sheet metal fabrication market, dramatic speed increases are realized with EZ Cut. A 20 percent increase in cutting speed compared to oxygen in 16-gauge (1.5 mm) mild steel is achieved in production. Cutting galvanized steel can be problematic with a CO2 laser due to the plasma formed from the zinc vapor interacting with the laser beam. With EZ Cut, this same thickness galvanized steel (16-gauge) is cut at 600 inches per minute as compared to 400 inches per minute using high-pressure nitrogen or even high-pressure compressed air.

The cutting conditions will need to be changed from using oxygen or high-purity nitrogen when using EZ Cut, but the cost savings both in edge finish, process speed or assist gas cost are tremendous.

Conclusion

An alternative to contaminated air from old and poorly maintained air supply and distribution systems is available today. Coupled with the ability to provide clean dry 95 percent pure nitrogen, users of this system can realize a considerable cost savings that will add profitability to their bottom line. Ultimately the ability to provide their customers with a faster turn-around time from raw material to finished part with an edge quality that eliminates the need to add a secondary operation will help keep customers coming back to place repeat orders.

Ancel Thompson is the Laser Division manager with Amada America Inc., Buena Park, CA, www.amada.com.

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